1. Field of the Invention
This invention relates to a coal-water slurry having a rheological additive which is the reaction product of a polycarboxylic organic acid and two or more hydroxylic compounds, one of which is necessarily a polyether glycol. The ester reaction product is employed in an amount from about 0.1 to about 4% by weight of the coal-water slurry, the slurry having from about 60 to about 80% by weight of solids, the balance being water.
2. Description of the Prior Art
In recent years a great deal of interest has developed in utilizing coal-water slurries in lieu of oil for electric power generation not only because of the lower cost of coal but also because ofits availability.
Coal-water slurries have been produced with solids contents of about 60 to about 75% which are fluid and handle in about the same way as petroleum fuels. These coal-water slurries may be burned directly wittout need of dewatering the mixture. The heat generated during combustion is sufficiency high so that the water in the slurry does not prevent it from being used to generate power. Naturally, as the solids of the coal-water slurry increase, the fuel value of the slurry also increases. For this reason, slurries having less than about 50 to 55% solids are unsuitable primarily for economic reasons.
One of the difficulties encountered with coal-water slurries at a solids content of about 60% and higher is that the dispersion of coal in water becomes an immobile mass and when burned it has to be handled in the same manner as lump coal. Handling in this respect includes not only transportation of the coal from the mine source but also the delivery of the coal to a combustion chamber such as the firebox of a steam boiler. Unless coal-water slurries have the same liquidity as oil at these higher solids content so that they may be transported by pipeline and injected into a firebox by spraying, the advantage of using a liquid carrier (i.e., water) for the coal is lost. Stated otherwise, the particles of coal in the slurry at these higher solids levels tend to convert the liquid carrier (water) into a plastic mass whereby the advantage of employing a liquid carrier is lost.
The prior art has overcome some of these difficulties by providing additives which may be used in relatively small amounts to assure that the coal-water slurry at high solids content is fluid. Examples of these additives are given by Kovacs in U.S. Pat. No. 4,435,306, Sakaria U.S. Pat. No. 4,398,919 and in European patent application Ser. No. 0131558. Coal-fuel oil slurries containing a dispersing agent are also described by Schmolka et al. in U.S. Pat. No. 4,288,232, Naka et al. U.S. Pat. No. 4,251,229 and Shimizu et al. U.S. Pat. No. 4,187,078.